When a signal arrives or ends there is a decision time to be added. This decision time ishighly dependent on the interface between communication and protection used. In manycases external interface (teleprotection equipment) is used. This equipment makes adecision and gives a binary signal to the protection device. In case of analog teleprotectionequipment typical decision time is in the range 10 – 30 ms. For digital teleprotectionequipment this time is in the range 2 – 10 ms.If the teleprotection equipment is integrated in the protection IED the decision time can beslightly reduced.Below the principle time sequence of signaling at current reversal is shown.ProtectionFunctionProtectionFunctionTele-ProtectionEquipmentTele-ProtectionEquipmentTele-communicationSystemCS from theprotectionfunction,operating andreset timeCS initiation tothecommunicationsystem, operatingand reset timeCS propagation,propagationCR selection anddecision,operating andreset timeCR to theprotectionfunction,operating andreset timeTimeFaultoccursProtectionpick-up CS initiationCR toteleprot.eq.CR toprot.func Fault currentreversalSendingprotectionresetCS tocommunicationdropCRreceptiondropCR toprot.funcdropMinimum setting of tDelay en05000536.vsdIEC05000536 V1 ENFigure 202: Time sequence of signaling at current reversal12.6.3.2 Weak-end infeedThe weak-end infeed can be set by setting the parameter WEI to Off, Echo or Echo &Trip. Operating zero sequence voltage when parameter WEI is set to Echo & Trip is setwith 3V0PU.The zero sequence voltage for a fault at the remote line end and appropriate fault resistanceis calculated.To avoid unwanted trip from the weak-end infeed logic (if spurious signals should occur),set the operate value of the broken delta voltage level detector (3V0) higher than the1MRK 506 334-UUS A Section 12Scheme communication411Application manual
